This invention relates to an adjustment mechanism for a fuel control apparatus through which fuel is supplied to an engine.
Such a fuel control apparatus is disclosed in U.S. Pat. No. 3,114,359 wherein the fuel flow to an engine is proportional to the mass air flow of the engine as measured by the forces generated across an air pressure diaphragm and a fuel pressure diaphragm. These forces which are opposite from each other are imposed on a control rod that is connected to a valve that controls the flow of fuel to the engine. It is desirable that all extraneous forces such as spring loads and frictional forces on the control rod be minimized in order to prevent the creation of a force inbalance between the air diaphragm and the fuel diaphragm. In particular, such extraneous forces are a problem when the force derived by the air pressure diaphragm is relatively small as, for example, at engine idle where fuel flow to the engine is at a minimum. One problem area through which such extraneous forces are introduced into the system is the fluid seal on the control rod which separates the pressurized fuel from the air.
In order to reduce the frictional drag imposed by the fluid seal between the fuel and air chamber, a balanced bellows seal as disclosed in U.S. Pat. No. 3,926,162 was devised. This bellows seal is completely adequate and operates effectively over the operating range of the fuel control valve.
As disclosed in U.S. Pat. No. 3,926,162 the position of the valve with respect to the valve seat can be adjusted through the use of shims in order that the valve engages the valve seat when the fuel diaphragm is in its neutral position. Unfortunately, in order to adjust the valve with respect to its valve seat the entire fuel control must be essentially dismantled and the shims installed. Such dismantling does not lend itself to the manufacture of a sufficient number of production units that is ordinarily required to make a profit.